First European High-Level Nuclear Waste Repository – OLKILUOTO, FINLAND – Rock Model Verification and Validation Calin Cosma & Nicoleta Enescu 7th International Workshop on the Application of Geophysics to Rock Engineering Lisbon 2007

Acknowledgements Timo Äikäs Liisa Wikström Kimmo Kemppainen Turo Ahokas Eero Heikkinen

What, Why, Where and When? Nuclear wastes don’t go away –the organic environment has to be protected at all times –the method shall not require continuous supervision and maintenance From all thinkable alternatives –there is an international concensus that –the geologic disposal has been proven to be the most suitable to provide safe isolation of the long-lived nuclear wastes Challenge of the geologic disposal –the time required for isolation, and thus for assessing the safety, is extremely long –due to long time required, considerable uncertainty is associated in the assesment

1980 – Start of programme for geologic storage in Finland Power companies responsible for activities and costPower companies responsible for activities and cost TVO starts to build an interim storage facilityTVO starts to build an interim storage facility International cooperation starts in the area of geologic disposal (Stripa)International cooperation starts in the area of geologic disposal (Stripa) Since the ‘90s, TVO has annually invested EUR million on research and development Since the ‘90s, TVO has annually invested EUR million on research and development

Issues for georesearch  Understanding groundwater is main research target –radionuclides can enter organic environment only by the transport of groundwater –chemical conditions can be influenced by groundwater related processes –performance of engineered barriers can be influenced by groundwater  In crystalline rock, essentially all groundwater transport takes place in fractures and fracture zones  Mapping the fracture zones is fundamental to evaluating the radionuclide transport from repository to the biosphere

Site Selection Research Programme Site identification Preliminary site characterisation Detailed site characterisation More than 100 candidate sites were identified

Nuclear Waste Disposal Project in Finland  The Olkiluoto site has been selected for deep geological disposal of spent nuclear fuel in 2001  Extensive geophysical data and imaging have been used to produce and refine a 3D model of the site  An underground research, testing and demonstration facility, ONKALO, is being built at Olkiluoto for detailed characterisation of the planned nuclear waste repository host rock. Tentative repository layout green, ONKALO yellow. The access tunnel will be 5.5 km long. Total length of tunnels for the research facility will be 8.3 km, at levels 420 m and 520 m.

Objectives of the geo-research programme Attain sufficient confidence in the plans for the final disposal operations Identification of bedrock volumes suited for final disposal Detailed definition of the properties of these volumes Mapping lithological contacts and structural features

The Olkiluoto Geological Model The almost twenty years of investigations have been recently implemented into geological model, where the geometric and parameter properties are given for four submodels (GeoMTF 2006):  Lithological model,  Ductile deformation model,  Brittle deformation model,  Alteration model. The bedrock at Olkiluoto consists of multiphase deformed and fractured granitic and gneissic rocks.

Geophysical Investigations at Olkiluoto Airborne and ground level geological mapping and geophysical soundings Surface and borehole seismic reflection imaging Detailed geophysical logging Core logging Hydrological and hydrochemical investigations 40 deep boreholes, over 7 km 2 were used Borehole investigations included Comprehensive geological mapping Geophysical logging, VSP, MSP and Crosshole seismic investigations, Detailed hydrological studies Ground level investigations included geological mapping on outcrops and in trenches, electrical, electromagnetic, magnetic, 3D reflection and refraction seismic surveys.

Integration/Confirmation – Bridging the scale – Detailed borehole logs & VSP The average trends observed from detailed borehole logging and from 3D VSP imaging display remarkable consistency. Lower hemisphere, equal-area stereographic projection. VSP reflectors are displayed in red, contours display fracture (and foliation) orientation distributions over depth ranges. A comparison of detailed borehole logging with the seismic investigations highlights the petrophysical and geological connection between features interpreted at different scales.

Model Confirmation from the ONKALO tunnel VSP predictions are being verified by direct observations

Model Confirmation from the ONKALO tunnel Direct observation of a sub-vertical deformed shear zone VSP reflector and VSP migrated sections from shots L15 and L25 measured from borehole KR04. Altered and deformed shear zone (green, transparent), and corresponding VSP reflector (black), same as shown in image A. Small grey disks on tunnel are other VSP reflectors. The weathered zone as observed in ONKALO wall at 280 m. A weathered and deformed shear zone oriented 110–170/40–60 (with an extension towards 150/36) has been met at tunnel length 240–282m and 450–453m, on investigation trenches at surface, and in boreholes. This zone is characterized by low seismic velocity.

Cross-validation of geological, hydrological, electrical and VSP models of a series of sub-horizontal brittle fault zones. Tunnel length 1355 m Model Confirmation from the ONKALO tunnel

3D rock features mapping by seismics Seismic features were found to be associated with: fracture zones fracture zones lithological contacts lithological contacts Reflectors without borehole control data may not directly be used as fracture zone indicators. From a subset of 29 most pro-eminent seismic features analyzed : 24 (83%) were unambiguously explained. 15 (50%) clearly identified as fracturing-related and 14 (50%) identified as combination of rock type/shearing and fracturing.

Conclusions Previous geophysical determinations, interpretations and models find confirmation by direct observation in the ONKALO tunnel. The main features met so far form a subset of the predictions made. The direct verification of the predictions shows a great potential of the group of investigations and interpretation techniques used so far. The direct verification of the predictions shows a great potential of the group of investigations and interpretation techniques used so far. Models built on large- and medium-scale investigations are easier to validate at the scale of the tunnel than in sparsely drilled boreholes. Models built on large- and medium-scale investigations are easier to validate at the scale of the tunnel than in sparsely drilled boreholes.

Olkiluoto today